We built an experimental apparatus which is able to produce a gas of Strontium atoms at ultra-low temperature T ~ 0.5µK in a microscopic confined volume (atomic trap). Our plan is to use ultra-cold Sr atoms as a quantum sensor to measure forces at micrometric distances from macroscopic source masses. In particular, our main goal is to investigate 1/r2 Newton's law in this range of length scales. This experiment is motivated by a number of recent theories beyond the Standard Model which suggest that gravity may deviate from Newton's law at sub millimeter length scales (hierarchy problem).
This experiment offers a novel competitive technique with respect to the present classical experiments which are based essentially on micro cantilevers or torsion pendula. The strong point of using atoms is the microscopic size of the force sensor which becomes smaller or comparable with length scales under investigation. Furthermore, using atoms as a quantum sensor opens the way for a future generation of experiments where the quantum mechanics will ultimately bring a dramatic improvement over the present classical techniques.
The recent availability of optical frequency-combs has made possible, for the first time, direct optical frequency measurements. This, in turn, opened the way to atomic clocks based on optical transitions which could be superior in accuracy and in stability compared with the actual microwave atomic standards. Among all possible atomic sources, a sample of neutral Sr atoms has been considered as one of the most interesting candidates because of the simple level scheme which presents a set of transitions well suited for laser cooling down to almost quantum degeneracy, as well as narrow linewidth clock-transitions (linewidth <1mHz for the fermionic 87Sr isotope). We intend to define a new frequency standard, referenced on visible transitions of atomic strontium.
